This invention relates to a line equalizer for use in automatically equalizing a line loss characteristic of a subscriber line.
A conventional line equalizer of the type described is proposed by Suzuki et al in IEEE Transactions on Communications, Vol. COM-30, No. 9, pages 2074-2082, and serves to equalize a line loss characteristic in response to an input signal given through a subscriber line. The line loss characteristic is variable in dependency upon temperature, humidity, and the like. The line equalizer is implemented by a switched capacitor circuit which has a plurality of frequency-gain characteristics corresponding to the variation of the line loss characteristic. The switched capacitor circuit uses a plurality of capacitors to provide the plurality of the frequency-gain characteristics.
Such a switched capacitor circuit is very effective when the bit rate or the data rate of the input signal is constant.
It is to be noted that various kinds of subscriber lines are used in a practical communication system to transmit data signals therethrough at different data rates or bit rates, such as for example, 3.2 kb/s, 6.4 kb/s, 12.8 kb/s, 64 kb/s, or 200 kb/s.
No consideration is directed to the case where the line equalizer is applied to such various subscriber lines of different data rates. Accordingly, a wide variety of switched capacitor circuits must be prepared so as to match the frequency-gain characteristics with the respective subscriber lines. Provision of such various switched capacitor circuits is very troublesome because the switched capacitor circuits must be individually manufactured.
In order to provide the frequency-gain characteristics for the respective subscriber lines through the use of a single line equalizer, a great number of capacitors would be formed in a semiconductor chip by an integrated circuit technique. This inevitably results in an increase of size in the semiconductor chip.